U.S. patent application number 13/464752 was filed with the patent office on 2012-12-06 for systems and methods for determining location of an access needle in a subject.
This patent application is currently assigned to University of Virginia Patent Foundation. Invention is credited to George T. Gillies, Srijoy Mahapatra, Jason Tucker-Schwartz.
Application Number | 20120310052 13/464752 |
Document ID | / |
Family ID | 47262190 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120310052 |
Kind Code |
A1 |
Mahapatra; Srijoy ; et
al. |
December 6, 2012 |
SYSTEMS AND METHODS FOR DETERMINING LOCATION OF AN ACCESS NEEDLE IN
A SUBJECT
Abstract
Systems and methods for epicardial electrophysiology and other
procedures are provided in which the location of an access needle
may be inferred according to the detection of different pressure
frequencies in separate organs, or different locations, in the body
of a subject. Methods may include inserting a needle including a
first sensor into a body of a subject, and receiving pressure
frequency information from the first sensor. A second sensor may be
used to provide cardiac waveform information of the subject. A
current location of the needle may be distinguished from another
location based on an algorithm including the pressure frequency
information and the cardiac waveform information.
Inventors: |
Mahapatra; Srijoy; (Edina,
MN) ; Gillies; George T.; (Charlottesville, VA)
; Tucker-Schwartz; Jason; (Nashville, TN) |
Assignee: |
University of Virginia Patent
Foundation
Charlottesville
VA
|
Family ID: |
47262190 |
Appl. No.: |
13/464752 |
Filed: |
May 4, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61482527 |
May 4, 2011 |
|
|
|
Current U.S.
Class: |
600/301 |
Current CPC
Class: |
A61B 5/04017 20130101;
A61B 2017/00243 20130101; A61B 5/02158 20130101; A61B 5/04014
20130101; A61B 5/02 20130101; A61B 5/061 20130101; A61B 5/065
20130101; A61B 2018/00577 20130101; A61B 5/02125 20130101; A61B
5/6848 20130101; A61B 17/3478 20130101; A61B 18/1492 20130101; A61B
5/0402 20130101; A61B 2018/00351 20130101; A61B 2034/2055 20160201;
A61B 5/725 20130101; A61B 17/3403 20130101; A61B 34/20 20160201;
A61B 2090/064 20160201; A61B 2562/0252 20130101; A61B 2562/0247
20130101; A61B 5/7203 20130101; A61B 5/02154 20130101 |
Class at
Publication: |
600/301 |
International
Class: |
A61B 5/02 20060101
A61B005/02 |
Claims
1. A method of inferring the location of a needle in a subject, the
method comprising: inserting a needle including a first sensor into
a body of a subject; receiving cardiac waveform information of the
subject from a second sensor; receiving pressure frequency
information from the first sensor; and distinguishing, by a
computer processor, a current location of the needle from another
location based on an algorithm including the pressure frequency
information and the cardiac waveform information.
2. The method of claim 1, further comprising: determining a
reference phase based on the cardiac waveform information;
determining a test phase based on the pressure frequency
information, wherein, said distinguishing is based on the pressure
frequency information from the test phase and the cardiac waveform
information from the reference phase.
3. The method of claim 1, wherein said distinguishing includes
comparing the algorithm results of the pressure frequency
information and the cardiac waveform information to a plurality of
predetermined threshold values.
4. The method of claim 1, wherein combining the pressure frequency
information and the cardiac waveform information includes phase
sensitive detection and matched filtering.
5. The method of claim 1, wherein combining the pressure frequency
information and the cardiac waveform information includes
integrating the pressure frequency information.
6. The method of claim 1, wherein the reference phase is a cardiac
phase of the subject immediately preceding the test phase.
7. The method of claim 1, wherein the cardiac waveform information
includes information derived from a plurality of cardiac phases of
the subject.
8. The method of claim 1, wherein the cardiac waveform information
includes at least one of ventricle pressure, arterial pressure, and
electrocardiogram (ECG) signals.
9. The method of claim 1, wherein the current location is a
non-pericardial location and the other location is a pericardial
location, or vice-versa.
10. The method of claim 1, wherein at least one of the current
location and the other location is a thorax of the subject.
11. The method of claim 1, wherein the method includes
distinguishing between a location remote from the pericardium, a
location close to or in contact with the pericardium, and a
location inside the pericardium.
12. The method of claim 1, wherein the method includes identifying
a location within ventricular tissue of the subject or inside the
interior of the heart of the subject.
13. A system for accessing one or more locations of a subject, said
device comprising: a needle having a distal end and a proximal end;
and a first sensor in communication with said needle for sensing
pressure frequency in the one or more locations of the subject; and
a processor configured to: receive cardiac waveform information of
the subject from a second sensor; receive pressure frequency
information from the first sensor; and distinguish a current
location of the needle from another location based on an algorithm
including the pressure frequency information and the cardiac
waveform information.
14. The system of claim 13, wherein the processor is further
configured to: determine a reference phase based on the cardiac
waveform information; and determine a test phase based on the
pressure frequency information, wherein, said distinguishing is
based on the pressure frequency information from the test phase and
the cardiac waveform information from the reference phase.
15. The system of claim 13, wherein said distinguishing includes
comparing the algorithm results of the pressure frequency
information and the cardiac waveform information to a plurality of
predetermined threshold values.
16. The system of claim 13, wherein combining the pressure
frequency information and the cardiac waveform information includes
phase sensitive detection and matched filtering.
17. The system of claim 13, wherein combining the pressure
frequency information and the cardiac waveform information includes
integrating the pressure frequency information.
18. The system of claim 13, wherein the reference phase is a
cardiac phase of the subject immediately preceding the test
phase.
19. The system of claim 13, wherein the cardiac waveform
information includes information derived from a plurality of
cardiac phases of the subject.
20. The system of claim 13, wherein the cardiac waveform
information includes at least one of ventricle pressure, arterial
pressure, and electrocardiogram (ECG) voltages.
21. The system of claim 13, wherein the current location is a
non-pericardial location and the other location is a pericardial
location, or vice-versa.
22. The system of claim 13, wherein at least one of the current
location and the other location is a thorax of the subject.
23. The system of claim 13, wherein the first sensor is
lockable.
24. A device for inferring the location of a needle in a subject,
said device comprising: a first input configured to receive
pressure frequency information from a first sensor disposed on a
distal end of the needle; a second input configured to receive
cardiac waveform information of the subject from a second sensor;
and a processor configured to: receive cardiac waveform information
of the subject from a second sensor; receive pressure frequency
information from the first sensor; and distinguish a current
location of the needle from another location based on an algorithm
including the pressure frequency information and the cardiac
waveform information.
25. The device of claim 24, wherein the processor is further
configured to: determine a reference phase based on the cardiac
waveform information; and determine a test phase based on the
pressure frequency information, wherein, said distinguishing is
based on the pressure frequency information from the test phase and
the cardiac waveform information from the reference phase.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority under 37 CFR .sctn.1.78(a)
to U.S. Provisional Application Ser. No. 61/482,527 filed on May 4,
2011, the contents of which are incorporated herein by reference in
their entirety.
[0002] The present application is related to the following
applications, of which all of the disclosures of the following
applications are hereby incorporated by reference herein in their
entireties:
[0003] PCT International Application Serial No. PCT/US2008/056643,
filed Mar. 12, 2008, entitled, "Access Needle Pressure Sensor
Device and Method of Use" and corresponding U.S. patent application
Ser. No. 12/530,830 filed Sep. 11, 2009;
[0004] PCT International Application Serial No. PCT/US2008/056816,
filed Mar. 13, 2008, entitled, "Epicardial Ablation Catheter and
Method of Use" and corresponding U.S. patent application Ser. No.
12/530,938 filed Sep. 11, 2009;
[0005] PCT International Application Serial No. PCT/US2008/057626,
filed Mar. 20, 2008, entitled, "Electrode Catheter for Ablation
Purposes and Related Method Thereof" and corresponding U.S. patent
application Ser. No. 12/532,233 filed Sep. 21, 2009;
[0006] PCT International Application Serial No. PCT/US2010/033189,
filed Apr. 30, 2010, entitled "Access Trocar and Related Method
Thereof";
[0007] PCT International Application Serial No. PCT/US2008/082835,
filed Nov. 7, 2008, entitled, "Steerable Epicardial Pacing Catheter
System Placed Via the Subxiphoid Process," and corresponding U.S.
patent application Ser. No. 12/741,710 filed May 6, 2010;
[0008] PCT International Application Serial No. PCT/US2010/061413,
filed Dec. 21, 2010, entitled "System For Femoral Vasculature
Catheterization and Related Method; and
[0009] PCT International Application Serial No. PCT/US2011/025470,
filed Feb. 18, 2011.
BACKGROUND OF THE INVENTION
[0010] Interest in epicardial (outer wall of the heart) treatment
of ventricular cardiac arrhythmias has grown significantly within
electrophysiology. The thickness of the myocardial wall makes it
difficult to treat all heart rhythm problems endocardially (from
inside the heart). Although early (pre-reperfusion era) data
suggested that epicardial ventricular tachycardia (VT) occurred in
a minority of patients, recent (non-ischemic VT and rapid
reperfusion era) data suggests that about 70% of VT patients have
epicardial substrates for the disease. Several studies have
suggested that epicardial ablation procedures are not only a viable
second line of defense when endocardial methods fail, but that
epicardial procedures should be performed in concert with all
endocardial treatments to guarantee the greatest probability of
treatment success of both ventricular tachycardia (which kills
500,000 Americans per year) and atrial fibrillation (which is the
largest cause of strokes in the U.S.). The epicardial surface is
also considered to be an important potential therapeutic location
for drug and cell delivery and as well as for heart failure
therapy.
[0011] The ability to gain minimally invasive access to the heart's
outer wall for ablation and other therapies has done much to
promulgate the adoption of epicardial strategies.
[0012] However, conventional types of guidance methods lead to an
unacceptable and high risk of perforations of the RV tissue. For
instance, Sosa and Scanavacca had an initial perforation rate of
8%, which decreased to 4.5% with experience. Others using this
approach have experienced 12% unsuccessful pericardial access, with
pericardial effusion in 13 of 35 cases and one death from
complications. Still another study suggested that 10 to 20% of all
patients undergoing pericardial access for epicardial ablation
using the methods described above experienced effusions due to some
level of ventricular perforation.
[0013] Therefore, it is a goal of an aspect of an embodiment of the
present invention to, among other things, improve the method of
access and reduce the risks of its use.
BRIEF SUMMARY OF THE INVENTION
[0014] Aspects of the present invention may find applicability in
systems and methods such as those described in, for example,
epicardial electrophysiology and other procedures in which the
location of an access needle may be inferred according to the
detection of different pressure frequencies in separate organs, or
different locations, in the body of a subject.
[0015] An aspect of an embodiment of the present invention may
provide, among other things, continuous measurements of the
pressure-frequency characteristics across the different regions of
the thorax. As discussed further herein, data of that type may be
used, for example, to determine how the thoracic pressure-frequency
waveform changes upon gaining proximity of and then traversing
through the parietal pericardial membrane. The inventors have found
that it can further be determined if the transition to a
two-component (intubation+heartbeat) signal was smooth and gradual,
or more abrupt in nature.
[0016] Aspects of the present invention may further provide, among
other things, improved instrumentation to collect continuous
segments of pericardial and non-pericardial pressure-frequency data
in vivo, in contrast to the discrete-location measurements. In
particular, an exemplary approach incorporates a high precision
fiber-optic sensor into the distal tip of the access needle, which
may replace the strain gauge sensor acted on by a fluid column
within a stationary sheath in an alternative embodiment.
[0017] Further aspects of the invention may provide, among other
things, an analysis algorithm, method, technique and system
designed to process pressure-frequency data so as to identify when
the needle's tip had safely entered, for example, the pericardial
space.
[0018] An aspect of an embodiment of the present invention may,
among other objects, reduce the clinical risks associated with
minimally invasive subxiphoid access, and thus improving the
reliability, safety and efficacy of it in the epicardial treatment
of cardiac arrhythmias and other clinical treatment paths involving
the pericardium and epicardial surface.
[0019] According to aspects of the invention, methods for inferring
the location of a needle in a subject may include one or more steps
of inserting a needle including a first sensor into a body of a
subject, receiving cardiac waveform information of the subject from
a second sensor, and receiving pressure frequency information from
the first sensor. Embodiments may include distinguishing, by a
computer processor, a current location of the needle from another
location and/or distinguishing the transition of the needle from a
first location to a second location, based on an algorithm
including the pressure frequency information and the cardiac
waveform information.
[0020] Embodiments may include determining a reference phase based
on the cardiac waveform information and/or determining a test phase
based on the pressure frequency information. In embodiments, the
distinguishing of location, and/or movement, of the needle may be
based on the pressure frequency information from the test phase and
the cardiac waveform information from the reference phase.
[0021] In embodiments, the distinguishing of location, and/or
movement, of the needle may include comparing the algorithm results
of the pressure frequency information and the cardiac waveform
information to a plurality of predetermined threshold values.
[0022] In embodiments, the combining of the pressure frequency
information and the cardiac waveform information may include phase
sensitive detection and matched filtering.
[0023] In embodiments, the combining of the pressure frequency
information and the cardiac waveform information may include
integrating the pressure frequency information.
[0024] In embodiments, the reference phase may be a cardiac phase
of the subject immediately preceding the test phase. In
embodiments, the cardiac waveform information may include
information derived from a plurality of cardiac phases of the
subject.
[0025] In embodiments, the cardiac waveform information may include
at least one of ventricle pressure, arterial pressure, pulse
oximetry, and electrocardiogram (ECG) signals.
[0026] In embodiments, the current location may be a
non-pericardial location and the other location may be a
pericardial location, or vice-versa. In embodiments, at least one
of the current location and the other location may be a thorax of
the subject.
[0027] Embodiments may also include distinguishing between a
location remote from the pericardium, a location close to or in
contact with the pericardium, and a location inside the
pericardium.
[0028] Embodiments may also include identifying a location within
ventricular tissue of the subject or inside the interior of the
heart of the subject.
[0029] According to further aspects of the invention systems for
accessing one or more locations of a subject may also be provided.
Such systems may include, for example, a needle having a distal end
and a proximal end and a first sensor in communication with the
needle for sensing pressure frequency in the one or more locations
of the subject. Embodiments may further include a processor
configured to perform various steps, such as those discussed
above.
[0030] For example, in embodiments, a processor may be configured
to receive cardiac waveform information of the subject from a
second sensor and receive pressure frequency information from the
first sensor. The processor may be further configured to
distinguish a current location of the needle from another location,
and/or the movement of the needle from one location to another,
based on an algorithm including the pressure frequency information
and the cardiac waveform information.
[0031] The processor may be further configured to determine a
reference phase based on the cardiac waveform information, and/or
determine a test phase based on the pressure frequency information.
The processor may be further configured to distinguish the location
and/or movement of the needle based on the pressure frequency
information from the test phase and the cardiac waveform
information from the reference phase.
[0032] In embodiments, the processor may be configured to compare
the algorithm results of the pressure frequency information and the
cardiac waveform information to a plurality of predetermined
threshold values.
[0033] In embodiments, the processor may be configured to combine
the pressure frequency information and the cardiac waveform
information using phase sensitive detection and matched
filtering.
[0034] In embodiments, the processor may be configured to integrate
the pressure frequency information as part of the combining of the
pressure frequency information and the cardiac waveform
information.
[0035] In embodiments, the processor may be configured such that
the reference phase is a cardiac phase of the subject immediately
preceding the test phase.
[0036] In embodiments, the processor may be configured such that
the cardiac waveform information includes information derived from
a plurality of cardiac phases of the subject.
[0037] In embodiments, the processor may be configured to receive
cardiac waveform information including at least one of ventricle
pressure, arterial pressure, pulse oximetry, and electrocardiogram
(ECG) voltages.
[0038] In embodiments, the processor may be configured to
distinguish between a non-pericardial location and a pericardial
location, a pericardial location and a thorax of the subject,
and/or between a pericardial location and a location within
ventricular tissue of the subject or inside the interior of the
heart of the subject.
[0039] According to further aspects of the invention, a device for
inferring the location of a needle in a subject may be provided
including a first input configured to receive pressure frequency
information from a first sensor and a second input configured to
receive cardiac waveform information of the subject from a second
sensor. In embodiments, the first sensor may be disposed proximate
to a distal end of the needle. Embodiments may further include a
processor in communication with the sensors, the processor
configured to perform steps such as those discussed above. For
example, the processor may be configured to receive cardiac
waveform information of the subject from the second sensor via the
second input and/or to receive pressure frequency information from
the first sensor via the first input. In embodiments, the processor
may be configured to distinguish a current location of the needle
from another location, and/or distinguish movement of the needle
from a first location to a second location, based on an algorithm
including the pressure frequency information and the cardiac
waveform information.
[0040] In embodiments, the processor may be further configured to
determine a reference phase based on the cardiac waveform
information, and determine a test phase based on the pressure
frequency information. The distinguishing may be based on the
pressure frequency information from the test phase and the cardiac
waveform information from the reference phase.
[0041] Additional features, advantages, and embodiments of the
invention may be set forth or apparent from consideration of the
following detailed description, drawings, and claims. Moreover, it
is to be understood that both the foregoing summary of the
invention and the following detailed description are exemplary and
intended to provide further explanation without limiting the scope
of the invention claimed. The detailed description and the specific
examples, however, indicate only preferred embodiments of the
invention. Various changes and modifications within the spirit and
scope of the invention will become apparent to those skilled in the
art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] The accompanying drawings, which are included to provide a
further understanding of the invention, are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the detailed description serve to
explain the principles of the invention. No attempt is made to show
structural details of the invention in more detail than may be
necessary for a fundamental understanding of the invention and
various ways in which it may be practiced. In the drawings:
[0043] FIG. 1 shows a chart of novel software algorithm, method,
and technique steps. Two parallel paths denote the analysis of the
reference waveform (left) and the input needle waveform
(right).
[0044] FIGS. 2A-2B show the ECG waveform segmentation. An example
ECG waveform (FIG. 2A solid line) is shown, as well as the
resulting segmentation points at the R wave (FIG. 2A dotted line).
The processed ECG according to the algorithm, method, and technique
in FIG. 1 is shown as well in FIG. 2B.
[0045] FIG. 3 shows the algorithm and method signal analysis.
Pericardial (left) and non-pericardial (right) examples of the
analysis of cardiac signal segments. Current cardiac segment (G),
previous cardiac segment interpolated and normalized (B), and
multiplied signals prior to integration (R).
[0046] FIG. 4 shows the average (dimensionless) test output values
for all 98 non-pericardial, 112 pericardial, and 5 ventricular
signals plotted on a log scale.
[0047] FIG. 5 shows the threshold analysis. The number of false
positives plotted against the number of false negatives for a range
of different threshold values for the algorithm analysis (open
circles) and the FFT analysis (closed circles).
[0048] FIG. 6 shows an example of the in vivo data. Algorithm and
method output for all signals from one animal, including the output
for all pericardial signals (open circles) and non-pericardial
signals (closed circles), as well as the presence of the thresholds
Ta (solid line) and Tb (dashed line), showing the separation of
signals.
[0049] FIG. 7 shows the threshold values and performance
characteristics of the algorithm compared to the FFT analysis.
[0050] FIG. 8 shows an indication of pericardial access. Incoming
signals from the fiber optic sensor in the access needle during a
ventilation hold (to suppress the breathing component of the
waveform), as the needle is moved through the parietal pericardial
membrane and into the pericardial space. An abrupt shift in the
frequency characteristics of the pressure signal becomes apparent
upon entry into the pericardium, as a large temporal signal
fluctuating at the frequency of the heart rate appears.
[0051] FIG. 9 is an illustration of an exemplary system according
to aspects of the invention, as used on a subject.
[0052] FIG. 10 is a schematic diagram of an exemplary access needle
according to aspects of the invention.
[0053] FIG. 11 is a schematic block diagram for a system or related
method of an embodiment of the present invention in whole or in
part.
DETAILED DESCRIPTION OF THE INVENTION
[0054] It is understood that the invention is not limited to the
particular methodology, protocols, and configurations, etc.,
described herein, as these may vary as the skilled artisan will
recognize. It is also to be understood that the terminology used
herein is used for the purpose of describing particular embodiments
only, and is not intended to limit the scope of the invention. It
also is be noted that as used herein and in the appended claims,
the singular forms "a," "an," and "the" include the plural
reference unless the context clearly dictates otherwise. Thus, for
example, a reference to "a sensor" is a reference to one or more
sensors and equivalents thereof known to those skilled in the
art.
[0055] Unless defined otherwise, all technical and scientific terms
used herein have the same meanings as commonly understood by one of
ordinary skill in the art to which the invention pertains. The
embodiments of the invention and the various features and
advantageous details thereof are explained more fully with
reference to the non-limiting embodiments and examples that are
described and/or illustrated in the accompanying drawings and
detailed in the following description. It should be noted that the
features illustrated in the drawings are not necessarily drawn to
scale, and features of one embodiment may be employed with other
embodiments as the skilled artisan would recognize, even if not
explicitly stated herein. Descriptions of well-known components and
processing techniques may be omitted so as to not unnecessarily
obscure the embodiments of the invention. The examples used herein
are intended merely to facilitate an understanding of ways in which
the invention may be practiced and to further enable those of skill
in the art to practice the embodiments of the invention.
Accordingly, the examples and embodiments herein should not be
construed as limiting the scope of the invention, which is defined
solely by the appended claims and applicable law. Moreover, it is
noted that like reference numerals reference similar parts
throughout the several views of the drawings.
[0056] Although various embodiments may be described in the context
of a subxiphoid access, and epicardial treatment, for clarity, the
invention encompasses and may be applied to other types of
treatment, particularly those taking place in, proximate to, and/or
or penetrating tissue or organs of the body including different
pressure frequency characteristics.
[0057] An aspect of an embodiment of the present invention system
(and related method) includes a precision fiber-optic pressure
sensor and a novel signal analysis algorithm, method, technique and
system for identifying pressure-frequency signatures which, in the
clinical setting, may allow for safer access to, for example, the
pericardial space.
[0058] As discussed further below, aspects of the invention include
instrumentation constituting the improved subxiphoid access system,
as well as the structure of the data analysis algorithm, method,
technique and system. Test results of the use of such systems and
methods are also provided based on a series of institutionally
approved in vivo trials of the intra-thoracic navigation of the tip
of a pressure-frequency sensing Tuohy needle in adult canines. The
inventors have further assessed the ability to limit the number of
residual false positive and false negative identifications of
needle location within the pericardium, as compared with the
empirical method as employed in the trials by a practicing
electrophysiologist.
Instrumentation
[0059] A series of ACUC approved animal trials were performed in
the University of Virginia vivarium by a practicing
electrophysiologist on ten canines (>22 kg), using the
standard-of-care pericardial access techniques currently employed
in the clinical Electrophysiology Lab. Anesthesia was induced using
fentanyl and etomidate, and maintained with isoflurane. Canines
were mechanically ventilated at a constant rate for the duration of
the trials, between 13 and 16 breaths per minute. For each animal,
a minimum of 4 pericardial access procedures were performed with a
standard 17 gauge epidural (Tuohy) needle. The clinician guided it
to the pericardium by fluoroscopy and injection of contrast agent.
In selected procedures the final pericardial location was verified
by placing a guide wire through the access needle's lumen and
observing its location under fluoroscopy. Hydrodynamic pressure
data from the access needle (>10 s records) were acquired during
each procedure at locations intra-thoracic prior to the diaphragm,
intra-thoracic after puncturing the diaphragm, and
intra-pericardial. The location of the needle, and therefore our
determination of each signal's pericardial or non-pericardial
nature, was identified by the clinician's judgment. Some of the
data were taken with the needle held in static positions, and the
rest while it was being moved from the thoracic cavity into the
pericardium, as well as upon withdrawal. Certain pressure
recordings were made with ventilation held to anatomically remove
breathing signals from the waveform.
[0060] During the access procedures, four simultaneous measurements
were acquired on a laboratory computer using LabVIEW
SignalExpress.TM. (National Instruments, Austin, Tex.). The four
measurements included the pressure as monitored by the sensor in
the needle's tip, the left ventricle (LV) pressure, the right
femoral artery (A-line) pressure, and the electrocardiogram (ECG)
voltages.
[0061] In an initial study of pericardial pressure dynamics, a
strain gauge on the proximal end of the access needle was used to
sense the pressures at the distal tip via a column of fluid between
it. Although such instrumentation is highly effective when utilized
properly for reading static pressure measurements from a single
location, it is difficult to employ for reading small-amplitude
hydrodynamic pressures when the fluid-filled conduit (be it a
sheath, catheter, or needle) is moving. This is because the fluid
filled column has weight, and hence the fluid's hydrostatic
pressure contributes inertial artifacts to the amplitude of the
pressure read at the proximal end of the fluid conduit. If the
needle's orientation relative to gravity is not maintained
unchanged while it is being advanced towards the pericardium, the
resulting fluctuations in the force transduced by the strain gauge
introduce substantial noise onto the signal. This makes the
technique very difficult to employ in the clinical setting during
an access procedure.
[0062] Therefore, a more viable method of monitoring pressures at
the tip of a dynamically shifting access needle is desired. In
embodiments, exemplary systems may include a solid-state, or
optical, pressure sensor. As used herein, "pressure sensors" may
preferably include sensors that are capable of registering not only
steady-state pressure, but also pressure frequency over time, which
may require rapid responsiveness and accuracy. In embodiments, such
sensors may also be understood as including, and/or in
communication with, a computer processor configured to determine
pressure frequency from pressure signals. Varying pressure
information received over a period of time may also be referred to
generally as pressure frequency information.
[0063] A fully solid-state sensor was implemented by the inventors
including a fiber optic (Fabry-Perot resonator) pressure transducer
(FISO, model FOP-MIV-BA-C1-F2-M2-R1-SC, Quebec, Canada), and was
introduced into the lumen of an access needle, with the transducer
tip placed just within the edge of the distal tip of the needle so
that it did not protrude into the tissue. The sensor at the distal
tip of the fiber had a diameter of 550 .mu.m. This was followed by
a 20-mm segment of bare fiber of roughly half the sensor's
diameter, with the remaining length encased in a PTFE sheath all
the way to the connector at the proximal end. The resolution was
.apprxeq.0.3 mm Hg, with a residual thermal drift of <-0.05%
.degree. C..sup.-1. In embodiments, a pressure sensor, such as an
optical sensor, may be affixed to, or proximate to, an end of an
access needle. As discussed further below, securing the pressure
sensor may be advantageous in reducing unwanted noise, but is not
necessarily required.
[0064] The optical fiber itself was fixed in place at the proximal
end of the needle by passing it through a Tuohy-Borst adapter which
was coupled onto the needle's Luer lock. In this instance, the
transducer was not fixed at the tip of the needle, since it had to
be removed from the inner lumen so that a guide wire could be
passed through the needle to verify the location inside the
pericardium. This was accomplished by decoupling the Tuohy-Borst
fitting from the needle's Luer lock and withdrawing the sensor.
During use, the fiber optic cable was connected to its mating light
source/signal conditioning device (FISO, model EVO/FPI-HR, Quebec,
Canada). The voltages from the analog output board on the signal
conditioner were read by an analog-to-digital data converter
(National Instruments, model USB-6009, Austin, Tex.) and stored for
subsequent analysis.
[0065] As mentioned above, three standard measures of cardiac
dynamics were acquired in synchrony with the needle pressures
during each trial. First, the LV pressures were monitored via a
clinical pigtail catheter, which was inserted into the left
ventricle from the animal's carotid artery. The pigtail catheter
was flushed and filled with saline, and the pressure in it was
monitored by a clinical flush-through transducer (Hospira, model
Transpac.TM., Lake Forest, Ill.). Second, central A-line pressures
were obtained via a 10 French sheath, placed in the femoral artery
of the canine The sheath was flushed and filled with saline, and
monitored by a transducer identical to that used in the LV pigtail
catheter. Both the LV and A-line transducers were connected to a
data acquisition and signal conditioning board (National
Instruments, model USB-9237, Austin, Tex.) via a custom-built cable
that bridged the RJ11 jack of the transducer wiring to the RJ50
input plug on the board. These resulting data were useful in
assessing the effect of cardiac dynamics on pericardial
pressures.
[0066] Third, electrophysiological data were taken during the
procedures. The bipolar electrical signal between leads on the
right arm (RA) and left arm (LA) was monitored by a custom-built
ECG reading system. The ionic potentials were transduced to
electronic potentials via standard clinical pediatric ECG
electrodes (Ambu.RTM., model Blue Sensor M, Glen Burnie, Md.). The
RA and LA leads were connected to a custom-built,
differential-amplifier signal conditioning circuit (Burr-Brown/TI
model OPA2227 P operational amplifiers, Dallas, Tex.) to buffer,
amplify, and bandpass-filter the incoming signal. The output signal
from the circuit was connected to the second port of the A/D data
acquisition device. The signals from both data acquisition units
were transferred to the laboratory computer via USB 2.0 connections
at a rate of .about.1.6 kHz by the LabVIEW SignalExpress.TM.
software.
Data Processing
[0067] Fast Fourier Transform Analysis
[0068] For each canine, a set of non-pericardial (pre-diaphragm and
post-diaphragm thoracic signals) and intra-pericardial signals were
collected. These signals were examined for segments with minimal
noise, and suitable samples 10 s long were extracted for further
analysis. A hanning window was applied to the segment, and a
linear-peak Fast Fourier Transform (FFT) was carried out in
LabVIEW. Using the embedded virtual instrument functions on the
same 10 s segment of any of the cardiodynamic reference signals,
the average heartbeat frequency for that segment was calculated,
and the magnitude of the FFT at that specific frequency point was
identified as the signal magnitude of interest at the heart rate.
Altogether, 98 non-pericardial and 112 pericardial signals were
collected and analyzed in this manner.
[0069] Following the collection of signal-magnitude data from all
210 signals, an automated search was performed to determine how
well a threshold value of the cardiac signal strength at the
heart-rate frequency could separate pericardial from
non-pericardial locations of the needle tip. A custom program in
MATLAB.RTM. was written and used to numerically evaluate the
magnitude data. The frequency component at the heart rate is
significantly less in the non-pericardial signal when compared to
the pericardial signal. The goal then was to define a threshold
pressure which indicated the best obtainable separation between
non-pericardial and pericardial signals by inferring the presence
of false positives and false negatives (i.e., non-pericardial
signals above the threshold, denoted by false.sub.p; pericardial
signals below the threshold, denoted by false.sub.n, respectively).
Possible threshold values were tested from the range of 0 to 0.6
mmHg (0 to 80 Pa), in increments of 0.0001 mmHg (0.013 Pa). For
each possible threshold value within that range, the number of
non-pericardial signal magnitudes above that threshold (false
positives) and the number of pericardial signal magnitudes below
that threshold (false negatives) were counted. The best obtainable
threshold was then found by minimizing the score
Score=W.sub.pfalse.sub.p+W.sub.nfalse.sub.n (1)
where the scoring weights W.sub.p and W.sub.n indicated the
relative importance of false positives and false negatives. In a
given calculation for best obtainable threshold, W.sub.p and
W.sub.n remain constant. A best obtainable threshold was found for
every combination of values of W.sub.p and W.sub.n ranging from 0.1
to 1.0 in increments of 0.1. The nature and application of the
findings is discussed below in the Results Section.
[0070] Custom Algorithm and Method Analysis
[0071] Additional investigations were conducted for determining if
a cardiac signal was present in the needle-tip signal, taking into
account the inconsistency of the heart rate in many of the
experiments and, in general, the spectral complexity of the
heartbeat signal. For example, heart-rate variability could not
only cause FFT spectral leakage, but even separate the FFT cardiac
peak into distinct sub-peaks of lower magnitude, making FFT-based
measurements inconsistent. Using the ECG as a reference signal, the
needle sensor's waveform was segmented between consecutive R waves
in the QRS complex of the signal. A custom-synthesized algorithm
that combined aspects of phase sensitive detection (PSD) and
matched filtering then analyzed it to ascertain the presence of a
consistent waveform with a fundamental frequency at that of the
heart rate, but with the ability to accommodate beat-to-beat
variations in heart rate. A flow chart for this algorithm is shown
in FIG. 1.
[0072] In FIG. 1, two parallel paths denote the analysis of the
reference waveform (left) and the input needle waveform (right).
Boxes are labeled as either a signal processing step (white
background) or a waveform (shaded background). The functions of the
blocks/elements in FIG. 1 are explained in detail below, and FIGS.
2 and 3 show the nature of the operation of the algorithm as the
data stream progresses through the blocks/elements of FIG. 1.
[0073] For the algorithm and method analysis, the same signals from
the FFT analysis were used for the algorithm and method analysis,
and an automated program in LabVIEW performed it on each of the
needle sensor's waveforms. After reviewing the spectral structure
of all the types of waveforms that were captured, none of which
contained signal components >100 Hz (which was taken to be the
Nyquist frequency), the signals were down-sampled to 2.times.100
Hz=200 Hz to allow for more precise filtering. All filtering
routines were performed in a zero-phase implementation, infinite
impulse response (IIR) mode, which filtered the forward signal and
then reversed and refiltered it, and reversed it again in order to
remove all phase-sensitive filtering transients. Moreover, all of
the simple high- and low-pass filters were of elliptic structure in
order to minimize the order of the filter, thus both minimizing
start- and end-signal transients and maximizing the computational
efficiency.
Reference Waveform Segmentation
[0074] The ECG waveform served as the reference for the algorithm
and method in identifying the timing of cardiac cycles in the
animal. The ECG signal segment was notch-filtered at 60 Hz
(Q.apprxeq.50) to eliminate any residual power-line noise that the
signal conditioner did not fully remove. The signal was then high
pass-filtered at a cutoff frequency of 20 Hz, to maintain only the
high frequency elements that compose the QRS complex. Then, the
strength of the remaining high-frequency noise components were
attenuated with an undecimated wavelet transform using a
biorthogonal 4.sub.--4 (FBI) wavelet to insure that only the QRS
peak of interest remained. To provide for consistency in subsequent
mathematical steps, the signal terms were then rectified by their
absolute value and the remaining detectable but extraneous peaks
were smoothed with a moving average filter. As shown in FIG. 2, the
surviving peaks were then identified as the R complex or the center
of the QRS complex in the cardiac cycles, in order to segment the
waveform into heartbeats according to the electrophysiology of the
patient.
[0075] FIG. 2 shows the ECG waveform segmentation. An example ECG
waveform (top, solid line) is shown, as well as the resulting
segmentation points at the R wave (top, dotted line). The processed
ECG according to the algorithm, method, and technique in FIG. 1 is
shown as well (bottom).
Analysis of the Pressure Waveform Produced by the Needle's
Sensor
[0076] The 10 s records of the needle's hydrodynamic pressure
signal were high-pass filtered with a cutoff frequency of 1 Hz to
attenuate low frequency breathing components. The resulting signal
was further separated into cardiac segments according to the timing
points found using the ECG analysis above. Only cardiac segments
containing a full cardiac cycle (a start and an end point) were
analyzed. A goal of the algorithm and method was to quantitatively
compare the waveform between consecutive cardiac segments. In many
implementations of phase-sensitive detection, the input waveform is
multiplied by a reference signal in order to evaluate whether the
waveform is of the desired frequency and phase. If the input
waveform's characteristics match those of the reference waveform,
then the multiplied signal will be perfectly rectified. For reasons
discussed below, in place of a common reference waveform which
would be used for that multiplication, the algorithm instead used
an interpolated version of the previous cardiac segment as the
reference waveform for the currently analyzed cardiac segment.
Examples of both pericardial and non-pericardial signals are shown
in FIG. 3.
[0077] FIG. 3 shows the algorithm and method signal analysis.
Pericardial (left) and non-pericardial (right) examples of the
analysis of cardiac signal segments. Current cardiac segment (G),
previous cardiac segment interpolated and normalized (B), and
multiplied signals prior to integration (R). Prior to that
multiplication, the previous cardiac segment was normalized to fit
between .+-.1 to insure uniformity of reference scale size. Then,
the area under the resulting signal segment was integrated to
arrive at an exact measure of the level of signal rectification. A
high positive output of the integration step correlated to a
significant signal with a fundamental frequency at the heart rate,
while other signals integrated towards zero. Because of the time
dependency of the integration process, the integrated output was
then multiplied by the fundamental frequency of that segment for
normalization in the time domain. A signal which is of higher
frequency will have a shorter integration time, and this is why the
integration is normalized by the frequency of the segment. The
outputs for each cardiac segment were then averaged over the 10 s
signal window. Algorithm thresholds were found using the same
scoring function as that employed for the FFT data as described
above.
[0078] This routine combines features of both match filtering and
PSD. If the main signal component which is present is fundamentally
matched to cardiac dynamics, then the signal should repeat between
cardiac segments, regardless of noise. It is assumed that if the
needle is in the pericardial space, then there should be good
agreement between the current and last cardiac segment of the
waveform. However, instead of convolving the signals or performing
Fourier multiplication of the signals, which is computationally
inefficient or requires a large window of consistent repeatable
signal, respectively, the signal may be integrated.
[0079] Another significant point is that when integrating a
high-noise signal, as more time points are integrated, the integral
of white noise tends to zero. Hence, this algorithm and method also
functions efficiently in high noise scenarios. In summary, this
approach, which employs the ECG as the reference waveform, is a
more elaborate but robust way of ascertaining the presence and
magnitude of a cardiac signal pattern in the needle sensor's
pressure signal, which can take into account and adjust for
irregular or inconsistent heart rates.
RESULTS
Average Signal Output
[0080] The signal magnitude at the heart rate frequency of the FFT
of the 98 non-pericardial waveforms was (0.09.+-.0.08) mmHg, and it
was (0.55.+-.0.31) mmHg for the 112 pericardial signals. Unpaired,
one-tailed t-tests revealed a statistically significant difference
in means of the two groups (p<0.01). Purposeful ventricular
perforation was successful in 5 animals, and the mean signal at the
heart rate from these 5 measurements was (24.98.+-.9.34) mmHg,
which was significantly greater than the magnitudes for both the
non-pericardial and pericardial groups (p<0.01).
[0081] The average, dimensionless signal output from the algorithm
for the 98 non-pericardial waveforms was (0.024.+-.0.03), and
(0.21.+-.0.14) for the 112 pericardial signals. Average signal
output for ventricular signals was (14.74.+-.5.97). As shown in
FIG. 4, all groups are significantly different from each other
(p<0.01).
Threshold Signal Separation
[0082] Using Eq. (1) on both the FFT and algorithm data, a number
of thresholds were found which separated the pericardial from the
non-pericardial data. However, this analysis also revealed some
overlap of non-pericardial and pericardial signals, i.e., regions
of non-separation of the signals (transition zone in FIG. 7). These
overlaps in signal strength may have been due to tissue clogs in
the needle lumen, imperfect localization of the sensor in or
outside of the pericardium, or the presence of a small cardiac
signal directly outside the pericardium. The latter-most option is
the most likely, especially if the needle is being pushed against
the pericardial surface, and therefore is in immediate proximity of
the heart. However, this range of signal overlap is important, and
suggests a need for three separation thresholds of cardiac signal
strength for the pericardial access procedure in the clinical
setting. These three thresholds would provide for the clinically
relevant separation of four regimes of pressure-frequency signal
dynamics: (i) away from the pericardium, (ii) very close to the
pericardium (the "transition" zone), (iii) safely inside the
pericardium, and (iv) dangerously within the ventricular tissue.
Moving from the thorax towards the heart, the first threshold,
T.sub.a, identifies the beginning of the transition zone, where a
small cardiac signal first arises. The second threshold, T.sub.b,
identifies the beginning of the pericardial zone, where the signal
structure is definitively pericardial. The third threshold,
T.sub.c, would indicate that there has been perforation of the
ventricle, which would be associated with a vast increase in
cardiac signal strength.
[0083] After analyzing both the FFT and algorithm data and method,
the values for thresholds T.sub.a and T.sub.b were selected. The
number of associated false positives and false negatives are
displayed in FIG. 7.
[0084] FIG. 7 shows the threshold values and performance
characteristics of an exemplary algorithm compared to the FFT
analysis. The exemplary algorithm and method is shown to be more
efficient at separating pericardial from non-pericardial signals,
as indicated by the decreased number of signals in the transition
zone between T.sub.a and T.sub.b, as well as the increase in the
number of signals which fall above or below the appropriate
threshold.
[0085] The separation of non-pericardial from pericardial signals
is the main focus in what follows. This is because the separation
of ventricular from non-ventricular signals is easily achieved for
T.sub.c without any false outputs. The performance of both the FFT
and algorithm analyses (and related methods) of the data is shown
in FIG. 5, which shows their relative abilities to limit both false
positives and false negatives over a range of threshold values.
[0086] False positives are more of a procedural nuisance than a
safety concern. On the other hand, false negatives are dangerous,
because the clinician might continue to advance the access needle
into the ventricle if the needle is actually pericardial but the
algorithm indicated that it was instead non-pericardial. Therefore,
one object of the invention is to not only minimize the total
number of false outputs (of both kinds), but to make the
minimization of false negatives the highest priority. The
custom-synthesized algorithm is able to minimize the number of
false negatives with much fewer false positives (see FIG. 5),
making it a more effective tool than FFT analysis for clinical
assessment of needle location using pressure-frequency guidance.
See Table I for representative values of T.sub.a and T.sub.b, and
see FIG. 6 for a plot of the signal outputs found for one of the
animals.
[0087] The resulting threshold values in the algorithm are 0.0405
for T.sub.a. 0.077 for T.sub.b, and 4 for T.sub.c. Of the 210
non-ventricular pressure measurements, 87.14% of the acquired
signals fell in the appropriate zone upon analysis with the
algorithm, with 1.43% of the signals identified as false negatives,
1.90% of the signals identified as false positives, and 9.52% of
the signals in the transition zone between T.sub.a and T.sub.b. All
5 (100%) ventricular measurements fell above T.sub.c, with no false
negatives or false positives regarding signals falling on the wrong
side of T.sub.c.
[0088] It is important to address the pericardial signal outputs
which fall beneath both T.sub.a and T.sub.b (i.e., the false
negatives shown in FIG. 7). Using an exemplary algorithm and
method, one of the false negatives from the FFT analysis was
remedied, because the algorithm was able to take into account the
complexity of the pericardial signal, while the FFT approach could
not. While there were still three false negatives assigned by the
algorithm, the inventors found that all were caused by the presence
of a large number of pre-ventricular contraction (PVC) beats.
Although the algorithms and methods used in this case were
efficient at handling solitary PVC beats in a given window, in each
of the three instances of false negatives the majority of the
waveform was composed of PVC beats. These beats caused lengthy
inconsistencies in the cardiac dynamics, making all of the
pressure-signal dynamics inconsistent as well. In all three
instances of false negatives for the algorithm, the time before the
signal is PVC-free, and the signal output occurs above T.sub.b in
the appropriate signal zone. This proved that these signals were
anatomically pericardial, but that the inconsistent cardiac
dynamics caused by the PVCs were impossible to track.
[0089] Thus, it was noted that it is possible that solitary PVC
beats may cause an error in the algorithm and method if only one
previous beat is used for comparison to the current cardiac
segment. In embodiments, such errors may be avoided, for example,
by adapting the algorithm to compare, for example, the previous two
to five beat segments. There are several ways in which it might be
accomplished, e.g. by acquiring and averaging the parameters of two
neighboring PVC beats and using that result to drive the
segmentation of the needle waveform. Other criteria may be applied
to disregard a reference phase. Such criteria may rely, for
example, on an appropriate statistical measure used to identify a
significantly irregular beat pattern (e.g., a sudden change in the
frequency band in which the beat occurred, indicating the
occurrence of what in nonlinear dynamics is called a "transition to
chaos").
[0090] In embodiments, the algorithm may be adapted to focus
primarily on capturing the first cardiac segment once the needle is
positioned pericardially. If one PVC beat were to occur at that
first segment, then the algorithm would simply have a delayed
response of one extra cardiac segment, and the probability of a PVC
occurring at such a precisely defined moment is very low.
[0091] Pericardial access can be critical for curing several
cardiac conditions but it is fraught with a high risk of both
procedural failure and ventricular perforation. To address these
issues, the inventors measured the pressure-frequency signals
generated by a solid state (fiber optic) sensor at the tip of a
pericardial access needle, and collected ECG signals in synchrony.
By employing a novel algorithm, method, technique and system that
contains characteristics of both matched filtering and
phase-sensitive detection to process those data, the location of
the needle's tip was distinguished accurately. In analogy with
phase sensitive detection, the present subject matter uses measures
of cardiac dynamics to separate the incoming needle's signal into
distinct sections. Also, just as matched filtering checks an
incoming signal according to a known outgoing signal, exemplary
algorithms according to aspects of the invention may be configured
to compare the current cardiac section of the signal to the
previous section, to search for a similar pattern. Such algorithms,
and associated methods, techniques and systems, can distinguish
pericardial from non-pericardial waveforms regardless of signal
dynamics and structure, as long as a signal with the fundamental
frequency (equal to the cardiac frequency) is present at any given
time. This is significant, because as different parts of the
pericardium are accessed at different needle insertion angles, the
signal structure can change.
[0092] It was found that the exemplary algorithms, and associated
methods, techniques and systems, presented herein provided a better
approach than tracking an FFT peak for several reasons. First, FFT
peaks take time to establish in a signal window, since they sample
global (and not local) frequency content. However, use of an
exemplary algorithm in systems such as those described is expected
to decrease the time lag needed to establishing the needle's
presence in the pericardium to just one cardiac cycle (i.e.,
.about.1 s).
[0093] In order to achieve such results, it is expected that a
sensor fixed, or locked, proximate to the end of the needle would
be advantageous. That is, configurations in which the fiber optic
sensor is left un-fixed within the tip of the needle (e.g. so that
it can be easily extracted whenever a guide wire had to be passed
into the needle's lumen), may result in some mechanical noise being
imposed on the signal based on the residual motion of the sensor's
tip. In order to reduce the overall effect of such noise, the
algorithm's output may also be averaged over an extended
window.
[0094] Also, as the patient's heart rate undergoes normal shifts,
both spectral leakage and separation of FFT peaks is a concern.
Since the systems and methods described herein track the patient's
cardiac dynamics directly, embodiments may also provide means of
tracking heart rate during accelerations into tachycardia,
decelerations into bradycardia, and inconsistencies as occur in
atrial fibrillation. Also, embodiments of the invention may be
useful for patients with low cardiac signal strength in the
pericardial waveform because of previous cardiac surgery and the
resulting pericardial adhesions.
[0095] Another important aspect of the invention is to quantify the
pressure waveform at the needle's tip as it breaches the
pericardial membrane, going from non-pericardial to pericardial
anatomy. In studying this, the inventors looked at several examples
of dynamic pressure measurements made while the needle both
breached into the pericardium and was pulled out of it were
acquired, and an example is shown in FIG. 8.
[0096] FIG. 8 shows an indication of pericardial access. Incoming
signals from the fiber optic sensor in the access needle during a
ventilation hold (to suppress the breathing component of the
waveform), as the needle is moved through the parietal pericardial
membrane and into the pericardial space. The signal transition
occurs just before the 8 second mark. It is evident that there is a
discrete addition of cardiac signal to the waveform at the point of
entering/leaving the pericardium. However, it is also evident that
there is a transition zone, which most likely occurs as the needle
is right outside the pericardium, which contains small levels of
cardiac signal, justifying the use of T.sub.a, to warn the
clinician they may in fact be close to the pericardium, although
not intra-pericardial.
[0097] According to aspects of the invention, embodiments may also
be adapted to allow for the analysis to occur in real time. Such
adaptation may include, among other features, real-time data
analysis during signal acquisition, as opposed to post-processing
of data segments. Also, a statistical analysis of this and other
pericardial and non-pericardial signals may be analyzed to
determine not clinical thresholds between anatomical zones, as well
as determining confidence intervals for those thresholds. This
would allow for systems and methods that tell the clinician which
anatomical zone they are in with statistical certainty. The needle
itself is also an important part of the access system that can be
improved to provide real-time or near real-time analysis. The
device used by the inventors was a Tuohy epidural needle, but with
the fiber optic sensor threaded through the lumen to the tip.
However, the pressure sensor was neither fixed to the tip of the
needle, nor designed to be otherwise housed by the Tuohy needle,
and this allowed the fiber optic tip to move in certain situations,
thus increasing noise and decreasing signal fidelity. A needle
with, for example, a fixed or locked pressure sensor would be
expected to produce readings with a larger signal-to-noise
ratio.
[0098] As discussed above, following in vivo studies on 10 adult
canine models, the inventors analyzed 215 pressure-frequency
measurements made at the distal tip of the access needle, of which
98 were from non-pericardial, 112 were from pericardial and 5 were
from ventricular locations. The needle locations as identified by
the exemplary systems and methods were significantly different from
each other (p<0.01), and systems and methods showed improved
performance when compared to a standard FFT analysis of the same
data. Moreover, the structure of the algorithm, method, technique
and system can be advantageously used to minimize, or overcome, the
time lags intrinsic to FFT analysis, such that the needle's
location may be determined in near-real time.
[0099] An advantage accruing from the use of the means and method
of the invention is, but not limited thereto, the ability to allow
for pacing of the epicardium itself with relative ease.
[0100] FIG. 9 shows a human subject 50 undergoing insertion of an
access needle 100 into the pericardial region 6 along a desired
pathway 5. The access needle 100 may include a pressure (or
pressure frequency) sensor disposed proximate to a distal end of
the needle. Other sensors (not shown) may also be disposed at or in
different locations of the subject 50, such as, for example ECG
sensors, and/or ventricle or arterial pressure sensors. The access
needle 100 can also be used to access the thorax 51 of the patient
50. The access can be accomplished by an interventional procedure,
such as a sub-xiphoid puncture, or a surgical procedure. It is
important during the procedure that critical organs and anatomical
structures within that region are not damaged by inadvertent
insertion of the access needle 100 into them during the needle
placement process. The physiological functions of the internal
organs, spaces and structures of the body within that region occur
at different levels of hydrostatic pressure. For instance, the
stomach 2 exerts a positive pressure (P.sub.+) on its bounding
structures, including the diaphragm 3. Meanwhile, the lung 1 will
function at negative pressures (P.sub.-) in the range of 5 to 10
atmospheres, with the heart 4 maintaining surface pressures of
approximately 12 mm Hg. Therefore, there are a variety of pressures
(as well as pressure frequencies) that might be sensed by the
access needle 100 during placement of it.
[0101] It should be appreciated that as discussed herein, a subject
may be a human or any animal. It should be appreciated that an
animal may be a variety of any applicable type, including, but not
limited thereto, mammal, veterinarian animal, livestock animal or
pet type animal, etc. As an example, the animal may be a laboratory
animal specifically selected to have certain characteristics
similar to human (e.g. rat, dog, pig, monkey), etc. It should be
appreciated that the subject may be any applicable human patient,
for example.
[0102] In an aspect of an embodiment of the invention, the access
needle 100 is used for accessing the thorax 51 and pericardium of a
subject 50, wherein the access needle comprises a pressure
frequency sensor or system for sensing pressure frequency in the
thorax, the pericardium or other tissue of the heart. However, it
should be appreciated that various embodiments of the present
invention device or system and method are not necessarily limited
to accessing the thorax and pericardium of a subject. It may also
be used in the organ structures or tubular structures in the thorax
as well as other locations or regions in the body. An organ
includes, for example, a solid organ, a hollow organ, parenchymal
tissue (e.g., stomach, brain, esophagus, colon, rectum, kidneys,
liver, etc.) and/or stromal tissue. Hollow organ structures
includes, for example, stomach, esophagus, colon, rectum, and
ducts, or the like. A tubular structure may include a blood vessel.
A blood vessel may include one or more of the following: vein,
venule, artery, arterial, or capillary.
[0103] FIG. 10 shows a schematic diagram of the details of
construction of one embodiment of said access needle 100. The
needle 100 has a distal end 300 and a proximal end 7. In some
embodiments, the needle 100 will have a length of about 10 to 25 cm
and will be of about 14 gauge size, but it could be smaller or
larger as suits the anatomy of the patient and the needs of the
clinician using it. The needle may have markings 8 nominally at
about 1 cm locations along its axial length. The markings can be
used to observe the depth of insertion of the needle 100 along the
pathway 5 shown in FIG. 9. At the proximal end 7 of the needle,
there can be at least one aperture, such as a plurality of channels
10 that provide means for achieving the functionalities of the
subject invention. These can include a port 11 to which the
manometry or pressure frequency sensing apparatus is connected
and/or a port 12 into which a guidewire, sheath, catheter, puncture
needle, or other devices or tools that may be inserted for passage
through and withdrawal from a distal aperture, such as an end port
hole 9. The puncture needle (not shown) can be in communication
with a spring and used to puncture tissue of a patient. A port 13
can be connected to a multi-channel structure, conduit or
connector, such as a three-way stopcock 15, for example, with inlet
ports 14 to allow entry and control of the flows of infusion agents
or desired fluid or medium. This flow can include providing a
fluid, liquid, gas, or mixtures thereof, with or without
therapeutic agents, drugs or the like, heating and/or cooling of
the fluid, chemical reactions and/or physical interactions between
the components of the fluid, and draining of the fluid. At the
distal end 300 of said needle 100, there can be an aperture, such
as a beveled end port hole 9. Said needle 100 might serve as the
placement mechanism for a sheath or catheter means 200, only the
distal portion of which is shown in FIG. 10. In another embodiment,
the sheath or catheter means 200 can be placed inside the needle
100. In one embodiment, the needle could have a divider running the
length of its axis, thus creating two or more zones, or lumens,
within it. One could be used for pressure frequency sensing, while
the other could be used for passage of a guide wire, catheter,
sheath, or puncture needle or other device or injection of a
contrast agent or other medium. The sensing component of the needle
could be much smaller in mean diameter than the other component,
with the sensing orifice positioned just in front of the other
component's orifice (or other locations, positions and sizes as
desired or required). As a result, if the sensing component
detected a perforation of the right ventricle, the resultant hole
created by the puncture devices or the like would thus be small.
Moreover, the entire distal tip of the inner needle assembly could
also be re-shaped so that it is similar to a Tuohy needle or some
other suitable configuration, thus further minimizing the risk of
inadvertent perforations.
[0104] Turning to FIG. 11, FIG. 11 is a functional block diagram
for a computer system 900 for implementation of an exemplary
embodiment or portion of an embodiment of present invention. For
example, a method or system of an embodiment of the present
invention may be implemented using hardware, software or a
combination thereof and may be implemented in one or more computer
systems or other processing systems, such as personal digit
assistants (PDAs) equipped with adequate memory and processing
capabilities. In an example embodiment, the invention was
implemented in software running on a general purpose computer 90 as
illustrated in FIG. 11. The computer system 900 may includes one or
more processors, such as processor 904. The Processor 904 is
connected to a communication infrastructure 906 (e.g., a
communications bus, cross-over bar, or network). The computer
system 900 may include a display interface 902 that forwards
graphics, text, and/or other data from the communication
infrastructure 906 (or from a frame buffer not shown) for display
on the display unit 930. For example, information indicating an
inferred location of an access needle, warnings related to an
inferred location, etc. Display unit 930 may be digital and/or
analog.
[0105] The computer system 900 may also include a main memory 908,
preferably random access memory (RAM), and may also include a
secondary memory 910. The secondary memory 910 may include, for
example, a hard disk drive 912 and/or a removable storage drive
914, representing a floppy disk drive, a magnetic tape drive, an
optical disk drive, a flash memory, etc. The removable storage
drive 914 reads from and/or writes to a removable storage unit 918
in a well known manner. Removable storage unit 918, represents a
floppy disk, magnetic tape, optical disk, etc. which is read by and
written to by removable storage drive 914. As will be appreciated,
the removable storage unit 918 includes a computer usable storage
medium having stored therein computer software and/or data.
[0106] In alternative embodiments, secondary memory 910 may include
other means for allowing computer programs or other instructions to
be loaded into computer system 900. Such means may include, for
example, a removable storage unit 922 and an interface 920.
Examples of such removable storage units/interfaces include a
program cartridge and cartridge interface (such as that found in
video game devices), a removable memory chip (such as a ROM, PROM,
EPROM or EEPROM) and associated socket, and other removable storage
units 922 and interfaces 920 which allow software and data to be
transferred from the removable storage unit 922 to computer system
900.
[0107] The computer system 900 may also include a communications
interface 924. Communications interface 124 allows software and
data to be transferred between computer system 900 and external
devices, including, for example, pressure sensors as described
herein, ECGs, etc. The communications interface 924 may include a
plurality of physical and/or virtual input/output ports configured
to communicate with different sensors, etc. Examples of
communications interface 924 may include a modem, a network
interface (such as an Ethernet card), a communications port (e.g.,
serial or parallel, etc.), a PCMCIA slot and card, a modem, wifi,
Bluetooth, etc. Software and data transferred via communications
interface 924 are in the form of signals 928 which may be
electronic, electromagnetic, optical or other signals capable of
being received by communications interface 924. Signals 928 are
provided to communications interface 924 via a communications path
(i.e., channel) 926. Channel 926 (or any other communication means
or channel disclosed herein) carries signals 928 and may be
implemented using wire or cable, fiber optics, blue tooth, a phone
line, a cellular phone link, an RF link, an infrared link, wireless
link or connection and other communications channels.
[0108] In this document, the terms "computer program medium" and
"computer usable medium" are used to generally refer to media or
medium such as various software, firmware, disks, drives, removable
storage drive 914, a hard disk installed in hard disk drive 912,
and signals 928. These computer program products ("computer program
medium" and "computer usable medium") are means for providing
software to computer system 900. The computer program product may
comprise a computer useable medium having computer program logic
thereon. The invention includes such computer program products. The
"computer program product" and "computer useable medium" may be any
computer readable medium having computer logic thereon.
[0109] Computer programs (also called computer control logic or
computer program logic) are may be stored in main memory 908 and/or
secondary memory 910. Computer programs may also be received via
communications interface 924. Such computer programs, when
executed, enable computer system 900 to perform the features of the
present invention as discussed herein. In particular, the computer
programs, when executed, enable processor 904 to perform the
functions of the present invention. Accordingly, such computer
programs represent controllers of computer system 900.
[0110] In an embodiment where the invention is implemented using
software, the software may be stored in a computer program product
and loaded into computer system 900 using removable storage drive
914, hard drive 912 or communications interface 924. The control
logic (software or computer program logic), when executed by the
processor 904, causes the processor 904 to perform the functions of
the invention as described herein.
[0111] In another embodiment, the invention is implemented
primarily in hardware using, for example, hardware components such
as application specific integrated circuits (ASICs). Implementation
of the hardware state machine to perform the functions described
herein will be apparent to persons skilled in the relevant
art(s).
[0112] In yet another embodiment, the invention is implemented
using a combination of both hardware and software.
[0113] In an example software embodiment of the invention, the
methods described above may be implemented in SPSS control language
or C++ programming language, but could be implemented in other
various programs, computer simulation and computer-aided design,
computer simulation environment, MATLAB, or any other software
platform or program, windows interface or operating system (or
other operating system) or other programs known or available to
those skilled in the art.
[0114] The description given above is merely illustrative and is
not meant to be an exhaustive list of all possible embodiments,
applications or modifications of the invention. Thus, various
modifications and variations of the described methods and systems
of the invention will be apparent to those skilled in the art
without departing from the scope and spirit of the invention.
Although the invention has been described in connection with
specific embodiments, it should be understood that the invention as
claimed should not be unduly limited to such specific embodiments.
Indeed, various modifications of the described modes for carrying
out the invention which are obvious to those skilled in the memory
circuit design, memory circuit manufacture or related fields are
intended to be within the scope of the appended claims.
[0115] The following patents, applications and publications as
listed below and throughout this document are hereby incorporated
by reference in their entirety herein.
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[0180] The disclosures of all references and publications cited
above are expressly incorporated by reference in their entireties
to the same extent as if each were incorporated by reference
individually.
* * * * *